diff --git a/plip_voice/main/CMakeLists.txt b/plip_voice/main/CMakeLists.txt
index b4ad37f..0ba7d89 100644
--- a/plip_voice/main/CMakeLists.txt
+++ b/plip_voice/main/CMakeLists.txt
@@ -11,9 +11,11 @@ idf_component_register(
         "dialer.c"
         "conversation.c"
         "turn_client.c"
+        "slic.c"
     INCLUDE_DIRS "."
     PRIV_REQUIRES
         driver
+        esp_driver_gpio
         esp_event
         esp_http_client
         esp_http_server
diff --git a/plip_voice/main/Kconfig.projbuild b/plip_voice/main/Kconfig.projbuild
index 618c037..81dff9d 100644
--- a/plip_voice/main/Kconfig.projbuild
+++ b/plip_voice/main/Kconfig.projbuild
@@ -38,10 +38,19 @@ menu "PLIP Voice Configuration"
 
     config PLIP_HOOK_GPIO
         int "Off-hook GPIO number"
-        default 4
+        default 23
         help
-            GPIO that signals handset off-hook (active LOW via INPUT_PULLUP).
-            Dev kit uses BOOT button (GPIO4 / KEY1). PCB uses Si3210 INT.
+            GPIO that signals handset off-hook.
+            SLIC SHK line is GPIO23 (A1S board KEY4, re-assigned to SLIC).
+            Legacy dev kit stub used GPIO4 (BOOT button, active-LOW).
+
+    config PLIP_HOOK_ACTIVE_HIGH
+        bool "Hook GPIO active-HIGH means off-hook"
+        default y
+        help
+            When enabled, a HIGH level on PLIP_HOOK_GPIO means the handset is
+            off-hook (SLIC SHK polarity).  When disabled, LOW means off-hook
+            (original dev-kit pull-up + BOOT button polarity).
 
     config PLIP_DIAL_PULSE
         bool "Enable rotary dial pulse decoding on SHK GPIO"
diff --git a/plip_voice/main/audio.c b/plip_voice/main/audio.c
index 3732452..573f934 100644
--- a/plip_voice/main/audio.c
+++ b/plip_voice/main/audio.c
@@ -428,7 +428,13 @@ esp_err_t audio_init(void)
         return ret;
     }
 
-    /* 3a. TX (speaker): Philips 16-bit stereo @ 16 kHz. */
+    /* 3a+3b. Full-duplex I2S config: SAME gpio_cfg for TX and RX.
+     * IDF5 i2s_std constitutes full-duplex ONLY when TX and RX configs are
+     * identical (memcmp). If they differ, on ESP32 HW v1 it tries to move
+     * RX to I2S_NUM_1, breaking clock routing and yielding permanent zeros.
+     * Fix: set both dout=PLIP_I2S_DOUT and din=PLIP_I2S_DIN in the same
+     * config and apply it to both handles. The IDF GPIO driver handles
+     * direction internally (dout→output, din→input). */
     i2s_std_config_t std_cfg = {
         .clk_cfg  = I2S_STD_CLK_DEFAULT_CONFIG(SAMPLE_RATE),
         .slot_cfg = I2S_STD_PHILIPS_SLOT_DEFAULT_CONFIG(
@@ -438,7 +444,7 @@ esp_err_t audio_init(void)
             .bclk = PLIP_I2S_BCLK,
             .ws   = PLIP_I2S_WS,
             .dout = PLIP_I2S_DOUT,
-            .din  = I2S_GPIO_UNUSED,
+            .din  = PLIP_I2S_DIN,
             .invert_flags = {
                 .mclk_inv = false,
                 .bclk_inv = false,
@@ -451,29 +457,7 @@ esp_err_t audio_init(void)
         ESP_LOGE(TAG, "i2s_channel_init_std_mode (TX): %s", esp_err_to_name(ret));
         return ret;
     }
-
-    /* 3b. RX (mic): same GPIO config as TX except DIN=GPIO35, DOUT=UNUSED.
-     * In full-duplex std mode, IDF requires the same BCLK/WS GPIOs to be
-     * specified in both TX and RX configs — it deduplicates GPIO matrix
-     * routing internally. Using UNUSED for BCLK/WS causes zero-data RX. */
-    i2s_std_config_t rx_cfg = {
-        .clk_cfg  = I2S_STD_CLK_DEFAULT_CONFIG(SAMPLE_RATE),
-        .slot_cfg = I2S_STD_PHILIPS_SLOT_DEFAULT_CONFIG(
-                        I2S_DATA_BIT_WIDTH_16BIT, I2S_SLOT_MODE_STEREO),
-        .gpio_cfg = {
-            .mclk = PLIP_I2S_MCLK,
-            .bclk = PLIP_I2S_BCLK,
-            .ws   = PLIP_I2S_WS,
-            .dout = I2S_GPIO_UNUSED,
-            .din  = PLIP_I2S_DIN,
-            .invert_flags = {
-                .mclk_inv = false,
-                .bclk_inv = false,
-                .ws_inv   = false,
-            },
-        },
-    };
-    ret = i2s_channel_init_std_mode(s_mic_handle, &rx_cfg);
+    ret = i2s_channel_init_std_mode(s_mic_handle, &std_cfg);
     if (ret != ESP_OK) {
         ESP_LOGE(TAG, "i2s_channel_init_std_mode (RX): %s", esp_err_to_name(ret));
         return ret;
diff --git a/plip_voice/main/board_config.h b/plip_voice/main/board_config.h
index 06ffbfc..9090423 100644
--- a/plip_voice/main/board_config.h
+++ b/plip_voice/main/board_config.h
@@ -40,3 +40,10 @@
 
 /* ---------- Off-hook GPIO (dev kit uses BOOT/KEY1 GPIO4 as stand-in) ---------- */
 /* Actual value comes from CONFIG_PLIP_HOOK_GPIO (Kconfig) */
+
+/* ---------- SLIC K50835F / AG1171-class front-end (A1S board wiring) ---------- */
+/* KEY3=GPIO19, KEY4=GPIO23, KEY5=GPIO18, KEY6=GPIO5 share these pins — reassigned to SLIC */
+#define PLIP_SLIC_RM    18   /* Ring Mode output — HIGH = ring burst active       */
+#define PLIP_SLIC_FR    5    /* Forward/Reverse output — toggled at 25 Hz for bell */
+#define PLIP_SLIC_SHK   23   /* Switch Hook input  — HIGH = off-hook (active-high) */
+#define PLIP_SLIC_PD    19   /* Power Down (open-drain) — HIGH = SLIC active       */
diff --git a/plip_voice/main/es8388.c b/plip_voice/main/es8388.c
index ce846c2..623d8c7 100644
--- a/plip_voice/main/es8388.c
+++ b/plip_voice/main/es8388.c
@@ -152,10 +152,14 @@ esp_err_t es8388_init(void)
      * - ADCCONTROL5 (0x0D) = 0x02: ADCFsMode SINGLE SPEED RATIO=256 (16kHz@MCLK 4.096MHz)
      * - ADCCONTROL8/9 (0x10/0x11) = 0x00: ADC digital volume 0dB */
     if (i2c_write_reg(ES8388_ADC_CTL1, 0xBB) != ESP_OK) return ESP_FAIL; /* PGA +24dB L+R */
-    if (i2c_write_reg(ES8388_ADC_CTL2, 0x00) != ESP_OK) return ESP_FAIL; /* LIN1/RIN1 differential (onboard mic) */
+    /* ADCCONTROL2 (0x0A): LINSEL/RINSEL = 0x00 → LINPUT1/RINPUT1 (LINE IN header on A1S kit)
+     * 0x00 = LIN1/RIN1 differential (standard LINE IN jack where AG1171 SLIC audio is wired)
+     * 0x50 = LIN2/RIN2 single-ended (onboard mic path — no SLIC signal here) */
+    if (i2c_write_reg(ES8388_ADC_CTL2, 0x00) != ESP_OK) return ESP_FAIL; /* LIN1/RIN1 differential (LINE IN / AG1171 SLIC) */
     if (i2c_write_reg(ES8388_ADC_CTL3, 0x02) != ESP_OK) return ESP_FAIL; /* DS filter sel */
     if (i2c_write_reg(ES8388_ADC_CTL4, 0x0C) != ESP_OK) return ESP_FAIL; /* I2S 16-bit */
     if (i2c_write_reg(ES8388_ADC_CTL5, 0x02) != ESP_OK) return ESP_FAIL; /* RATIO=256 */
+    if (i2c_write_reg(0x0E, 0x00) != ESP_OK) return ESP_FAIL; /* ADCCONTROL6: clear ADCSMUTE bit5 (reset default 0x30 = ADC output muted) */
     if (i2c_write_reg(ES8388_ADC_CTL8, 0x00) != ESP_OK) return ESP_FAIL; /* ADC vol L 0dB */
     if (i2c_write_reg(ES8388_ADC_CTL9, 0x00) != ESP_OK) return ESP_FAIL; /* ADC vol R 0dB */
 
@@ -173,11 +177,12 @@ esp_err_t es8388_init(void)
     if (i2c_write_reg(ES8388_DAC_CTL17, 0x90) != ESP_OK) return ESP_FAIL;
     if (i2c_write_reg(ES8388_DAC_CTL20, 0x90) != ESP_OK) return ESP_FAIL;
 
-    /* 11. DACCONTROL21 (0x2B): ADC+DAC LRCK sync = 0xC0 (both ADC and DAC share LRCK).
-     * Espressif reference: 0xC0 when both ADC and DAC active (record+playback mode).
-     *                      0x80 when DAC only.
-     * This register is a clock routing register, NOT a volume register. */
-    if (i2c_write_reg(ES8388_DAC_CTL21, 0xC0) != ESP_OK) return ESP_FAIL;
+    /* 11. DACCONTROL21 (0x2B): ADC+DAC LRCK sync.
+     * Espressif reference es8388_start():
+     *   0xC0 = LINE mode (analog bypass, not ADC digital path)
+     *   0x80 = DAC+ADC digital record+playback mode (bit7 only)
+     * We want digital ADC recording + DAC playback → use 0x80. */
+    if (i2c_write_reg(ES8388_DAC_CTL21, 0x80) != ESP_OK) return ESP_FAIL;
 
     /* 11b. Restart internal state machine (required after DACCONTROL21 change).
      * Without this pulse, the ADC clock domain may not synchronise properly.
@@ -198,9 +203,12 @@ esp_err_t es8388_init(void)
     /* 13. DAC power: power up DAC L+R. */
     if (i2c_write_reg(ES8388_DAC_POWER, 0x3C) != ESP_OK) return ESP_FAIL;
 
-    /* 14. ADC power: power up ADC (0x09 per Espressif reference).
-     * Must come AFTER DACCONTROL21 state machine restart and all ADC register writes. */
-    if (i2c_write_reg(ES8388_ADC_POWER, 0x09) != ESP_OK) return ESP_FAIL;
+    /* 14. ADC power: full power-up (all Pdn bits cleared = 0x00).
+     * 0x09 is the intermediate state (Espressif es8388_open end-state), but
+     * the full ADC + analog input power-up requires 0x00 (Espressif es8388_start(ADC)).
+     * Must come AFTER DACCONTROL21 state machine restart and ADCCONTROL6 unmute. */
+    if (i2c_write_reg(ES8388_ADC_POWER, 0x00) != ESP_OK) return ESP_FAIL;
+    vTaskDelay(pdMS_TO_TICKS(10));  /* let ADC analog settle after full power-up */
 
     /* 15. Enable PA (power amplifier for speaker). */
     gpio_set_direction(PLIP_PA_ENABLE, GPIO_MODE_OUTPUT);
@@ -216,7 +224,7 @@ esp_err_t es8388_init(void)
     es8388_read_reg(ES8388_CHIP_POWER,   &chippower);
     ESP_LOGI(TAG, "ES8388 regs: CTL1=0x%02X ADCPWR=0x%02X ADCINSEL=0x%02X ADCCTL3=0x%02X DACCTL21=0x%02X CHIPPOWER=0x%02X",
              ctl1, adcpwr, adcinsel, adcctl3, dacctl21, chippower);
-    ESP_LOGI(TAG, "ES8388 init OK — PA enabled, DAC @ 0dB, ADC PGA +24dB, input=LIN1, DACCTL21=0xC0");
+    ESP_LOGI(TAG, "ES8388 init OK — PA enabled, DAC @ 0dB, ADC PGA +24dB, input=LIN1/RIN1 (LINE IN), DACCTL21=0x80");
     return ESP_OK;
 }
 
diff --git a/plip_voice/main/main.c b/plip_voice/main/main.c
index 9b38563..740ae26 100644
--- a/plip_voice/main/main.c
+++ b/plip_voice/main/main.c
@@ -24,11 +24,13 @@
 #include "freertos/FreeRTOS.h"
 #include "freertos/task.h"
 
+#include "board_config.h"
 #include "audio.h"
 #include "net.h"
 #include "cmd_exec.h"
 #include "hook_client.h"
 #include "phone.h"
+#include "slic.h"
 #include "scenario_mesh.h"
 #include "dialer.h"
 #include "conversation.h"
@@ -60,8 +62,18 @@ static void boot_task(void *arg)
 {
     (void)arg;
 
+    /* ── 1b. SLIC power-up (before audio — PD must be released early) ── */
+    esp_err_t ret = slic_init();
+    if (ret != ESP_OK) {
+        ESP_LOGE(TAG, "slic_init FAILED: %s — SLIC remains in power-down (no audio path, no hook sense)",
+                 esp_err_to_name(ret));
+    } else {
+        ESP_LOGI(TAG, "SLIC powered up: PD=GPIO%d OD-HIGH, SHK=GPIO%d active-HIGH, RM=GPIO%d, FR=GPIO%d",
+                 PLIP_SLIC_PD, PLIP_SLIC_SHK, PLIP_SLIC_RM, PLIP_SLIC_FR);
+    }
+
     /* ── 2. Audio init (Phase A) ── */
-    esp_err_t ret = audio_init();
+    ret = audio_init();
     if (ret != ESP_OK) {
         ESP_LOGE(TAG, "audio_init FAILED: %s", esp_err_to_name(ret));
         ESP_LOGE(TAG, "PHASE A BLOCKED — check ES8388 I2C wiring (SDA=33, SCL=32)");
diff --git a/plip_voice/main/net.c b/plip_voice/main/net.c
index 1f1a20c..3cdc570 100644
--- a/plip_voice/main/net.c
+++ b/plip_voice/main/net.c
@@ -26,7 +26,11 @@
 
 #include "audio.h"
 #include "cmd_exec.h"
+#include "phone.h"
 #include "es8388.h"
+#include "slic.h"
+#include "board_config.h"
+#include "driver/gpio.h"
 #include "esp_err.h"
 #include "esp_event.h"
 #include "esp_http_server.h"
@@ -429,6 +433,40 @@ static esp_err_t handle_cmd_post(httpd_req_t *req)
     return send_json(req, "200 OK", "{\"ok\":true}");
 }
 
+/* ── GET /debug/ring  (trigger ring tone over HTTP) ──────────────────────── */
+
+static esp_err_t handle_debug_ring(httpd_req_t *req)
+{
+    phone_ring_start();
+    ESP_LOGI(TAG, "debug/ring: ring started");
+    return send_json(req, "200 OK", "{\"ok\":true,\"ringing\":true}");
+}
+
+/* ── GET /debug/ringstop  (stop ring tone over HTTP) ─────────────────────── */
+
+static esp_err_t handle_debug_ringstop(httpd_req_t *req)
+{
+    phone_ring_stop();
+    ESP_LOGI(TAG, "debug/ringstop: ring stopped");
+    return send_json(req, "200 OK", "{\"ok\":true,\"ringing\":false}");
+}
+
+/* ── GET /debug/slic  (read GPIO levels of all 4 SLIC pins) ──────────────── */
+
+static esp_err_t handle_debug_slic(httpd_req_t *req)
+{
+    char buf[192];
+    /* gpio_get_level reads the actual pad level even for output pins. */
+    snprintf(buf, sizeof(buf),
+             "{\"rm\":%d,\"fr\":%d,\"shk\":%d,\"pd\":%d,\"offhook\":%s,\"ringing\":%s}",
+             gpio_get_level(PLIP_SLIC_RM), gpio_get_level(PLIP_SLIC_FR),
+             gpio_get_level(PLIP_SLIC_SHK), gpio_get_level(PLIP_SLIC_PD),
+             slic_is_offhook() ? "true" : "false",
+             slic_is_ringing() ? "true" : "false");
+    ESP_LOGI(TAG, "debug/slic: %s", buf);
+    return send_json(req, "200 OK", buf);
+}
+
 /* ── GET /debug/dial?number=NNNN  (push digits into the dialer) ───────────── */
 
 static esp_err_t handle_debug_dial(httpd_req_t *req)
@@ -527,7 +565,7 @@ esp_err_t net_init(void)
     /* Start HTTP server. */
     httpd_config_t hcfg = HTTPD_DEFAULT_CONFIG();
     hcfg.server_port      = 80;
-    hcfg.max_uri_handlers = 14;
+    hcfg.max_uri_handlers = 17;
     hcfg.stack_size       = 8192;
 
     esp_err_t ret = httpd_start(&s_httpd, &hcfg);
@@ -564,6 +602,18 @@ esp_err_t net_init(void)
         .uri = "/debug/dial", .method = HTTP_GET,
         .handler = handle_debug_dial, .user_ctx = NULL,
     };
+    static const httpd_uri_t uri_debug_ring = {
+        .uri = "/debug/ring", .method = HTTP_GET,
+        .handler = handle_debug_ring, .user_ctx = NULL,
+    };
+    static const httpd_uri_t uri_debug_ringstop = {
+        .uri = "/debug/ringstop", .method = HTTP_GET,
+        .handler = handle_debug_ringstop, .user_ctx = NULL,
+    };
+    static const httpd_uri_t uri_debug_slic = {
+        .uri = "/debug/slic", .method = HTTP_GET,
+        .handler = handle_debug_slic, .user_ctx = NULL,
+    };
     httpd_register_uri_handler(s_httpd, &uri_status);
     httpd_register_uri_handler(s_httpd, &uri_scenario);
     httpd_register_uri_handler(s_httpd, &uri_file);
@@ -571,7 +621,10 @@ esp_err_t net_init(void)
     httpd_register_uri_handler(s_httpd, &uri_capture);
     httpd_register_uri_handler(s_httpd, &uri_debug_regs);
     httpd_register_uri_handler(s_httpd, &uri_debug_dial);
+    httpd_register_uri_handler(s_httpd, &uri_debug_ring);
+    httpd_register_uri_handler(s_httpd, &uri_debug_ringstop);
+    httpd_register_uri_handler(s_httpd, &uri_debug_slic);
 
-    ESP_LOGI(TAG, "httpd up on :80 (GET /status, GET /debug/regs, GET /debug/dial, POST /game/scenario, POST /game/file, POST /game/cmd, POST /voice/capture)");
+    ESP_LOGI(TAG, "httpd up on :80 (GET /status, GET /debug/regs, GET /debug/dial, GET /debug/ring, GET /debug/ringstop, GET /debug/slic, POST /game/scenario, POST /game/file, POST /game/cmd, POST /voice/capture)");
     return ESP_OK;
 }
diff --git a/plip_voice/main/phone.c b/plip_voice/main/phone.c
index 984e59c..eee7653 100644
--- a/plip_voice/main/phone.c
+++ b/plip_voice/main/phone.c
@@ -19,6 +19,7 @@
 #include "audio.h"
 #include "hook_client.h"
 #include "conversation.h"
+#include "slic.h"
 
 #if CONFIG_PLIP_DIAL_PULSE
 #include "dialer.h"
@@ -52,7 +53,10 @@ void phone_ring_start(void)
 {
     if (s_ringing) return;
     s_ringing = true;
-    ESP_LOGI(TAG, "ring start");
+    ESP_LOGI(TAG, "ring start: SLIC RM/FR + audio tone");
+    /* Physical bell via SLIC RM/FR (main ringer) */
+    slic_ring_start();
+    /* Optional in-earpiece audio tone (audible feedback when handset is up) */
     audio_ring_start();
 }
 
@@ -60,7 +64,8 @@ void phone_ring_stop(void)
 {
     if (!s_ringing) return;
     s_ringing = false;
-    ESP_LOGI(TAG, "ring stop");
+    ESP_LOGI(TAG, "ring stop: SLIC RM/FR off + audio stop");
+    slic_ring_stop();
     audio_stop();
 }
 
@@ -70,6 +75,26 @@ static void report_offhook(bool offhook)
     hook_client_report(offhook ? "off" : "on", offhook ? "pickup" : "hangup");
 }
 
+/*
+ * Hook polarity:
+ *   CONFIG_PLIP_HOOK_ACTIVE_HIGH=y  (default, SLIC SHK GPIO23): HIGH = off-hook
+ *   CONFIG_PLIP_HOOK_ACTIVE_HIGH=n  (legacy BOOT button GPIO4): LOW  = off-hook
+ *
+ * Rotary pulse notes (SLIC SHK, active-HIGH):
+ *   Off-hook base: SHK HIGH.  A rotary pulse briefly opens the loop → SHK drops LOW
+ *   for ~60-100 ms, then returns HIGH.  Hangup: SHK stays LOW for >500 ms.
+ *   So "open" (pulse event) = level drops LOW when active-HIGH polarity.
+ */
+#if CONFIG_PLIP_HOOK_ACTIVE_HIGH
+#define HOOK_OFFHOOK_LEVEL  1   /* HIGH = off-hook */
+#define HOOK_PULSE_OPEN     0   /* LOW  = rotary pulse open (loop broken) */
+#define HOOK_PULSE_CLOSED   1   /* HIGH = rotary pulse closed (loop restored) */
+#else
+#define HOOK_OFFHOOK_LEVEL  0   /* LOW  = off-hook (legacy pull-up + BOOT button) */
+#define HOOK_PULSE_OPEN     1   /* HIGH = rotary pulse open */
+#define HOOK_PULSE_CLOSED   0   /* LOW  = rotary pulse closed */
+#endif
+
 static void phone_task(void *arg)
 {
     (void)arg;
@@ -88,9 +113,11 @@ static void phone_task(void *arg)
 
     /* Read and report initial level so master state machine is in sync. */
     int last_level = gpio_get_level(hook_gpio);
-    s_offhook = (last_level == 0);
-    ESP_LOGI(TAG, "phone task ready, hook GPIO=%d level=%d (%s)",
-             hook_gpio, last_level, s_offhook ? "off-hook" : "on-hook");
+    s_offhook = (last_level == HOOK_OFFHOOK_LEVEL);
+    ESP_LOGI(TAG, "phone task ready, hook GPIO=%d level=%d active_%s (%s)",
+             hook_gpio, last_level,
+             (HOOK_OFFHOOK_LEVEL == 1) ? "high" : "low",
+             s_offhook ? "off-hook" : "on-hook");
 
     if (!s_offhook) {
         ESP_LOGI(TAG, "boot: on-hook -> PA off (mute)");
@@ -104,11 +131,12 @@ static void phone_task(void *arg)
     conversation_on_hook_change(s_offhook);
 
 #if CONFIG_PLIP_DIAL_PULSE
-    /* Rotary pulse state */
+    /* Rotary pulse state.
+     * With SLIC SHK (active-HIGH): off-hook = HIGH, pulse = brief LOW dip. */
     int     pulse_count   = 0;
-    bool    in_pulse      = false;   /* GPIO is currently high (open) */
-    int64_t pulse_open_us = 0;       /* timestamp when GPIO went high */
-    int64_t last_close_us = 0;       /* timestamp when GPIO last went low (closed) */
+    bool    in_pulse      = false;   /* true while SHK is in pulse-open state */
+    int64_t pulse_open_us = 0;       /* timestamp when pulse open started */
+    int64_t last_close_us = 0;       /* timestamp when pulse closed (SHK back to OFFHOOK) */
 #endif
 
     for (;;) {
@@ -119,19 +147,19 @@ static void phone_task(void *arg)
             /* While off-hook, use fast polling instead of 30ms debounce
              * so rotary pulses (~60-100ms) are not missed. */
             if (s_offhook) {
-                /* The ISR fired — re-read immediately to catch rising edge. */
+                /* The ISR fired — re-read immediately to catch the edge. */
                 vTaskDelay(pdMS_TO_TICKS(5));  /* minimal settle */
                 int level = gpio_get_level(hook_gpio);
 
-                if (level == 1 && last_level == 0) {
-                    /* Rising edge: GPIO went open */
-                    last_level    = 1;
+                if (level == HOOK_PULSE_OPEN && last_level == HOOK_PULSE_CLOSED) {
+                    /* Pulse open: loop broken (SHK dropped from off-hook level) */
+                    last_level    = HOOK_PULSE_OPEN;
                     in_pulse      = true;
                     pulse_open_us = esp_timer_get_time();
                     ESP_LOGD(TAG, "pulse: open");
-                } else if (level == 0 && last_level == 1) {
-                    /* Falling edge: GPIO closed again */
-                    last_level    = 0;
+                } else if (level == HOOK_PULSE_CLOSED && last_level == HOOK_PULSE_OPEN) {
+                    /* Pulse closed: loop restored */
+                    last_level    = HOOK_PULSE_CLOSED;
                     last_close_us = esp_timer_get_time();
                     int64_t open_dur_ms = (last_close_us - pulse_open_us) / 1000;
 
@@ -155,12 +183,12 @@ static void phone_task(void *arg)
                 goto poll_sleep;
             }
 #endif
-            /* Standard 30 ms debounce for on-hook state transitions */
+            /* Standard 30 ms debounce for on-hook/off-hook transitions */
             vTaskDelay(pdMS_TO_TICKS(DEBOUNCE_MS));
             int level = gpio_get_level(hook_gpio);
             if (level != last_level) {
                 last_level = level;
-                if (level == 0) {
+                if (level == HOOK_OFFHOOK_LEVEL) {
                     /* Off-hook: handset picked up. */
                     s_offhook = true;
 #if CONFIG_PLIP_DIAL_PULSE
@@ -168,7 +196,8 @@ static void phone_task(void *arg)
                     in_pulse      = false;
                     last_close_us = esp_timer_get_time();
 #endif
-                    ESP_LOGI(TAG, "off-hook (pickup) detected — PA on");
+                    ESP_LOGI(TAG, "off-hook (pickup) detected — PA on, SLIC offhook=%d",
+                             slic_is_offhook());
                     audio_pa_set(true);
                     phone_ring_stop();
                     report_offhook(true);
@@ -185,7 +214,7 @@ static void phone_task(void *arg)
 
 #if CONFIG_PLIP_DIAL_PULSE
         /* Check for inter-digit gap: if we accumulated pulses and the line
-         * has been closed (quiet) for > MAX_GAP_MS, emit the digit. */
+         * has been at closed (off-hook) state for > MAX_GAP_MS, emit the digit. */
         if (s_offhook && pulse_count > 0 && !in_pulse && last_close_us > 0) {
             int64_t gap_ms = (esp_timer_get_time() - last_close_us) / 1000;
             if (gap_ms > CONFIG_PLIP_DIAL_PULSE_MAX_GAP_MS) {
@@ -201,14 +230,15 @@ static void phone_task(void *arg)
             }
         }
 
-        /* Also detect prolonged open (hangup) even if no more edges arrive */
+        /* Also detect prolonged open (hangup) even if no more edges arrive.
+         * Active-HIGH: hangup = level stays at HOOK_PULSE_OPEN (LOW) > 500 ms. */
         if (s_offhook && in_pulse && pulse_open_us > 0) {
             int64_t open_ms = (esp_timer_get_time() - pulse_open_us) / 1000;
             if (open_ms >= HANGUP_THRESHOLD_MS) {
                 int level_now = gpio_get_level(hook_gpio);
-                if (level_now == 1) {
+                if (level_now == HOOK_PULSE_OPEN) {
                     ESP_LOGI(TAG, "on-hook (prolonged open %"PRId64"ms) detected", open_ms);
-                    last_level  = 1;
+                    last_level  = HOOK_PULSE_OPEN;
                     pulse_count = 0;
                     in_pulse    = false;
                     s_offhook   = false;
@@ -216,8 +246,8 @@ static void phone_task(void *arg)
                     audio_pa_set(false);
                     report_offhook(false);
                 } else {
-                    /* GPIO closed already but ISR missed it */
-                    last_level    = 0;
+                    /* GPIO returned to off-hook level but ISR missed it */
+                    last_level    = HOOK_PULSE_CLOSED;
                     last_close_us = esp_timer_get_time();
                     if ((esp_timer_get_time() - pulse_open_us) / 1000 < HANGUP_THRESHOLD_MS) {
                         pulse_count++;
diff --git a/plip_voice/main/slic.c b/plip_voice/main/slic.c
new file mode 100644
index 0000000..7d80dc6
--- /dev/null
+++ b/plip_voice/main/slic.c
@@ -0,0 +1,150 @@
+/*
+ * slic.c — K50835F / AG1171-class SLIC control (ESP-IDF port).
+ *
+ * Ported from hardware/projects/slic-phone/src/slic/Ks0835SlicController.cpp
+ * (Arduino) to bare ESP-IDF 5.x GPIO driver.
+ *
+ * Key differences from Arduino original:
+ *  - Open-drain on PD achieved via GPIO_MODE_OUTPUT_OD + gpio_set_level(PD, 1)
+ *  - Ring FR toggle runs as a FreeRTOS task instead of a cooperative tick()
+ *  - hook_active_high is hard-coded TRUE (matches A252ConfigStore default)
+ */
+
+#include "slic.h"
+#include "board_config.h"
+
+#include "driver/gpio.h"
+#include "esp_log.h"
+#include "freertos/FreeRTOS.h"
+#include "freertos/task.h"
+
+#define TAG "slic"
+
+/* Active-high hook polarity: HIGH on SHK = off-hook.
+ * Source: hardware/projects/slic-phone/src/config/A252ConfigStore.cpp:262
+ *   cfg.hook_active_high = true; */
+#define SLIC_SHK_OFFHOOK_LEVEL  1
+
+static volatile bool s_ringing = false;
+static TaskHandle_t  s_ring_task = NULL;
+
+/* ── FR toggle task (ring drive at ~25 Hz) ────────────────────────────────── */
+
+static void slic_ring_task(void *arg)
+{
+    (void)arg;
+    bool fr_state = false;
+
+    for (;;) {
+        if (s_ringing) {
+            fr_state = !fr_state;
+            gpio_set_level(PLIP_SLIC_FR, fr_state ? 1 : 0);
+            ESP_LOGV(TAG, "FR=%d", fr_state ? 1 : 0);
+        } else {
+            /* Suspended — keep FR low while idle */
+            gpio_set_level(PLIP_SLIC_FR, 0);
+            fr_state = false;
+        }
+        vTaskDelay(pdMS_TO_TICKS(20));   /* 20 ms → ~25 Hz */
+    }
+}
+
+/* ── Public API ──────────────────────────────────────────────────────────── */
+
+esp_err_t slic_init(void)
+{
+    /* RM: Ring Mode output, init LOW */
+    gpio_config_t rm_cfg = {
+        .pin_bit_mask = (1ULL << PLIP_SLIC_RM),
+        .mode         = GPIO_MODE_OUTPUT,
+        .pull_up_en   = GPIO_PULLUP_DISABLE,
+        .pull_down_en = GPIO_PULLDOWN_DISABLE,
+        .intr_type    = GPIO_INTR_DISABLE,
+    };
+    esp_err_t ret = gpio_config(&rm_cfg);
+    if (ret != ESP_OK) return ret;
+    gpio_set_level(PLIP_SLIC_RM, 0);
+
+    /* FR: Forward/Reverse output, init LOW */
+    gpio_config_t fr_cfg = {
+        .pin_bit_mask = (1ULL << PLIP_SLIC_FR),
+        .mode         = GPIO_MODE_OUTPUT,
+        .pull_up_en   = GPIO_PULLUP_DISABLE,
+        .pull_down_en = GPIO_PULLDOWN_DISABLE,
+        .intr_type    = GPIO_INTR_DISABLE,
+    };
+    ret = gpio_config(&fr_cfg);
+    if (ret != ESP_OK) return ret;
+    gpio_set_level(PLIP_SLIC_FR, 0);
+
+    /* SHK: Switch Hook input with pull-up (physical line has no external pull) */
+    gpio_config_t shk_cfg = {
+        .pin_bit_mask = (1ULL << PLIP_SLIC_SHK),
+        .mode         = GPIO_MODE_INPUT,
+        .pull_up_en   = GPIO_PULLUP_ENABLE,
+        .pull_down_en = GPIO_PULLDOWN_DISABLE,
+        .intr_type    = GPIO_INTR_DISABLE,
+    };
+    ret = gpio_config(&shk_cfg);
+    if (ret != ESP_OK) return ret;
+
+    /* PD: Power Down — push-pull output HIGH = SLIC active (definite power-up).
+     * Previous config (open-drain HIGH) left the line floating when no pull-up
+     * is present on the bench, keeping the SLIC in power-down.
+     * Push-pull HIGH drives the PD pin firmly high regardless of external resistors. */
+    gpio_config_t pd_cfg = {
+        .pin_bit_mask = (1ULL << PLIP_SLIC_PD),
+        .mode         = GPIO_MODE_OUTPUT,         /* push-pull (pas OD) */
+        .pull_up_en   = GPIO_PULLUP_DISABLE,
+        .pull_down_en = GPIO_PULLDOWN_DISABLE,
+        .intr_type    = GPIO_INTR_DISABLE,
+    };
+    ret = gpio_config(&pd_cfg);
+    if (ret != ESP_OK) return ret;
+    ret = gpio_set_level(PLIP_SLIC_PD, 1);   /* HIGH franc = SLIC actif */
+    if (ret != ESP_OK) return ret;
+
+    ESP_LOGI(TAG, "slic: PD GPIO%d push-pull HIGH (SLIC power-up, franc)", PLIP_SLIC_PD);
+    ESP_LOGI(TAG, "slic: pins RM=%d FR=%d SHK=%d PD=%d hook_active_high=1",
+             PLIP_SLIC_RM, PLIP_SLIC_FR, PLIP_SLIC_SHK, PLIP_SLIC_PD);
+
+    /* Spawn the FR-toggle task (runs indefinitely, toggles only when s_ringing=true) */
+    BaseType_t ok = xTaskCreatePinnedToCore(slic_ring_task, "slic_ring",
+                                             2048, NULL, 4, &s_ring_task, 1);
+    if (ok != pdPASS) {
+        ESP_LOGE(TAG, "Failed to create slic_ring task");
+        return ESP_ERR_NO_MEM;
+    }
+
+    int shk = gpio_get_level(PLIP_SLIC_SHK);
+    ESP_LOGI(TAG, "SLIC init OK — SHK level=%d (%s)",
+             shk, (shk == SLIC_SHK_OFFHOOK_LEVEL) ? "off-hook" : "on-hook");
+    return ESP_OK;
+}
+
+bool slic_is_offhook(void)
+{
+    return gpio_get_level(PLIP_SLIC_SHK) == SLIC_SHK_OFFHOOK_LEVEL;
+}
+
+void slic_ring_start(void)
+{
+    if (s_ringing) return;
+    ESP_LOGI(TAG, "ring start: RM=HIGH, FR toggling at 25 Hz");
+    gpio_set_level(PLIP_SLIC_RM, 1);
+    s_ringing = true;
+}
+
+void slic_ring_stop(void)
+{
+    if (!s_ringing) return;
+    ESP_LOGI(TAG, "ring stop: RM=LOW, FR=LOW");
+    s_ringing = false;
+    gpio_set_level(PLIP_SLIC_RM, 0);
+    gpio_set_level(PLIP_SLIC_FR, 0);
+}
+
+bool slic_is_ringing(void)
+{
+    return s_ringing;
+}
diff --git a/plip_voice/main/slic.h b/plip_voice/main/slic.h
new file mode 100644
index 0000000..8f39928
--- /dev/null
+++ b/plip_voice/main/slic.h
@@ -0,0 +1,59 @@
+/*
+ * slic.h — K50835F / AG1171-class SLIC control (ESP-IDF port of Ks0835SlicController).
+ *
+ * Pins (A1S board, from board_config.h):
+ *   RM  GPIO18  Ring Mode output     — HIGH = ring burst active
+ *   FR  GPIO5   Forward/Reverse out  — toggled at ~25 Hz during ring to drive bell
+ *   SHK GPIO23  Switch Hook input    — HIGH = off-hook (active-high)
+ *   PD  GPIO19  Power Down (OD)      — HIGH = SLIC powered (released open-drain)
+ *
+ * Power-up: PD is open-drain, written HIGH → high-impedance → SLIC active.
+ * Power-down: PD driven LOW → SLIC off (no audio, no hook sense).
+ *
+ * Ring: slic_ring_start() sets RM=1 and spawns/enables a 20 ms FR-toggle task.
+ *       slic_ring_stop()  clears RM=0, FR=0, pauses the toggle task.
+ *
+ * Hook: slic_is_offhook() reads SHK; HIGH = off-hook (matches A252ConfigStore default).
+ */
+
+#pragma once
+
+#include <stdbool.h>
+#include "esp_err.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * Initialise SLIC GPIO and power up the SLIC.
+ * Must be called early in boot, before audio init.
+ * Returns ESP_OK on success.
+ */
+esp_err_t slic_init(void);
+
+/**
+ * Returns true when the handset is off-hook (SHK GPIO23 HIGH).
+ */
+bool slic_is_offhook(void);
+
+/**
+ * Activate ringing: RM=HIGH + FR toggles at ~25 Hz (20 ms period).
+ * No-op if already ringing.
+ */
+void slic_ring_start(void);
+
+/**
+ * Stop ringing: RM=LOW, FR=LOW, FR toggle suspended.
+ * No-op if not ringing.
+ */
+void slic_ring_stop(void);
+
+/**
+ * Returns true if slic_ring_start() was called and not yet stopped.
+ */
+bool slic_is_ringing(void);
+
+#ifdef __cplusplus
+}
+#endif
diff --git a/plip_voice/sdkconfig.defaults b/plip_voice/sdkconfig.defaults
index 20540ad..b6f354d 100644
--- a/plip_voice/sdkconfig.defaults
+++ b/plip_voice/sdkconfig.defaults
@@ -35,6 +35,10 @@ CONFIG_ESP_TASK_WDT_TIMEOUT_S=15
 # when I2S/WiFi interrupts spill into idle stack on original ESP32.
 CONFIG_FREERTOS_IDLE_TASK_STACKSIZE=2048
 
+# SLIC hook GPIO — SHK on GPIO23 (A1S KEY4, active-HIGH: HIGH = off-hook)
+CONFIG_PLIP_HOOK_GPIO=23
+CONFIG_PLIP_HOOK_ACTIVE_HIGH=y
+
 # WiFi credentials — set via `idf.py menuconfig` (PLIP Voice Configuration)
 # or override locally in sdkconfig (NOT committed).
 # CONFIG_PLIP_WIFI_SSID="..."